Humble Earthworm. Introduction and characteristics.

Almost every one will be familiar with the humble earthworm, that our American friends call the night crawler. But how many are aware of their fascinating characteristics, lifestyle, structure, or about their breeding, feeding, enemies and other fascinating facts. They do not possess eyes, arms, legs, or lungs, yet they breathe oxygen in order to survive as we as a species are required to do.

Earthworms belong to the order Haplotaxida and the family Lumbricidae. There are about 33 species around the world. Lumbricus terrestris is the common European earthworm, they are also known as " dew worm " in some regions.

The general characteristics of the earthworm are these---Earthworms occur in great numbers in almost all soils. Even if one does not see the creature, its presence may be confirmed by the little heaps of soil, known as worm casts, which are thrown up at the opening of their burrows. These worm casts are composed of soil which the worm has eaten and then passed through the body, in doing so it extracts whatever nutrients from it that are available.

Another way one may detect the unseen presence of worms is available to the more observant among us, { especially gardeners} by the creatures habit, by the creatures habit of dragging leaves, leaf stalks, small twigs and other similar objects into their burrows. these may be detected at the opening of their burrows where the objects may project vertically in the air. Clusters of the above named objects may be encountered.

A leaf with its point in the opening of a worms burrow.

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General information

Studies have revealed, that during the above mentioned operation, the leaf is nearly always dragged into the burrow by the pointed end, which is of course the easiest way to drag it into a hole. { does this show a sense of intelligence on the worms part?}. Being nocturnal creatures this operation is usually undertaken at night. the operation takes a considerable period of time to complete. Why do worms carry out this operation at all ?. They procure for themselves a store of food which they can eat at their leisure below the surface out of sight of their many predators { see Food and Senses below} and secondly an equally important reason-they prevent entry into their burrows of smaller predators, and keep the air within relatively moist, but at the same time allowing air to enter, thus allowing fresh air to enter, providing ventilation for necessary breathing .

The Body for the most part is cylindrical and is marked with a number of circular grooves, corresponding number of rings or segments which closely resemble each other. The segments become gradually of less diameter so that the head extremity is finely tapered. Nature has deemed this to be so, and for a good reason. It means that the worm can start to burrow in the tiniest of crevices , then bore a hole that is sufficiently large enough for the rest of the body to pass through. The rear end of the worm is flattened considerably so that it is wider than any other part of the body.

This may look mis-shaped to our eyes and perception, however, nature has an economy that has nothing to waste and everything has a good reason for existing. For the most part the worm we see upon the lawn appears to be fully exposed, and completely out of their burrows. However, the tail is is still firmly secured in the confines of the burrow and maintains a firm pressure on the walls. At the slightest alarm the worm darts back into the burrow with an amazing speed thus the life of the worm is saved many times by this employment.

Worm casts in grassland.

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Breathing and colour.

The colour of the most common earthworms is pinkish or purplish red. The colour of course is not the colour of the creatures actual skin, but rather, the blood that shows though the skin. This red colouring matter is similar to our own and performs the same function, that is to say extracting oxygen from the atmosphere and carry it to all parts of the body.

For our part the oxygen is obtained as the blood passes through the lungs. Worms on the other hand do not possess lungs so the oxygen is obtained by being absorbed directly through the skin. This is made possible by the skin itself being extremely thin, and, kept moist by its own slime. In addition there is in every segment a special set of blood vessels which pass very close under the skin, this brings the blood as close to the surface as is possible. These blood vessels start from the main blood vessel which is visible through the skin as a dark red line that runs up the middle of the back.

Movement.

When moving along the worm does not wriggle from side to side in the manner of a snake, but rather in a straight line.This is achieved by the creature lengthening and shortening its body alternately, the whole or successive parts of its body. To achieve this locomotion their needs to be some sort of grip upon the surface of the soil. This grip is undertaken by the use of bristles called setae which the creature can employ from beneath its body. Each segment has eight pairs of setae two on the left and two on the right hand side.

Thus movement is attained by pushing the front of the body forwards, the bristles then dart out to grip the equalities of the soil { You will never see worms climbing up glass in the manner of a slug for instance} The hind region is then pulled forward and then the bristles beneath this part of the body take the grip and the front end is pushed forward once more, and so on and so on.

Breeding---

The body of the adult earthworm is swollen and thickened at a location about a quarter of the total body length from the front end.The size of this swelling differs in various species. It would be prudent at this point to dispel a myth associated with this swelling. It has long been a misconception that these swellings are the result of injury or where the body has been reunited after being bisected with a spade, should this unfortunate occurrence befall the worm it would die!.

The true function is concerned with breeding. The skin in this region produces a girdle of tough slime completely encircling the body. out of this girdle the worm wriggles backwards and deposits within its cavity its own eggs and the fertilising element received from another worm.In time when the worm has completely withdrawn its head from the girdle the two open ends of the girdle close up, and the structure is left in the ground as a lemon-shaped cocoon, containing around six eggs. An average cocoon will produce only one young worm and the other eggs will perish. The presence of this swelling often referred to as the saddle indicates that the worm has reached maturity.

It is an interesting fact that all worms are Hermaphrodites, that is to say they possess both male and female organs. The male openings are situated on the right hand side of the 15th segment and may be detected by the presence of thickened lips surrounding the actual holes. The female organs through which the eggs pass are in the corresponding places in the 14th segment, but, are generally very difficult to detect.

Earthworm showing the swelling known as the saddle.

Courtesy of Michael Linnenbach CC BY-SA 2.0 license.

Food and senses.

The food, as already mentioned, largely consists of decaying vegetable matter, and also vegetable matter in the soil, but living leaves may also feature if there are any within the creatures reach.Since the worm possess no teeth it is necessary for them to soften the leaf before they can tear any bits from it with their lips. To achieve this aim a slime is pored over the leaf from the front part of its body and possibly also from the mouth. The slime possesses the power of rotting and partly digesting the vegetable tissue, so that the subsequent removal of the lips is easier.

The worm is also stone death, but on the other hand is extremely sensitive to vibration in the soil. There is little doubt that this ability warns many of them of approaching moles. Again because the creature has no eyes, but, the skin as a whole but even more so at the front of the body can distinguish between darkness and light. This can be demonstrated by flashing a bright light on to an undisturbed worm at night. As soon as the light is detected it recoils its body.

Defence and enemies.

To a soft bodied creature such as the worm a discreet retreat is the best form of defence. However ,even the humble earthworm has some defensive tricks at its disposal. The slime which covers the whole of its upper body makes the creature very slippery and difficult to grasp. This often helps it to escape the eager beaks of thrushes and other birds. a large number of their foes are parasitic and abound in the upper surface of the soil where the earthworm inhabits in large numbers. many of these are microscopic and are caught and covered in slime which kills them. Some of them are completely destroyed by the antiseptic properties which it possesses.

Should this defence be inadequate the worm has yet another line of defence. From minute holes that open from the grooves along the body, one hole in the middle of the back of each groove, gushes out when such action is required. It is a watery fluid in which float numerous corpuscles possessing the capability of independent movement. These corpusles swarm around the microscopic foes and destroy them.

The effects of weather on the Earthworm

During periods of drought or of frost worms retreat from the surface layers of the soil into the deeper layers often descending several feet in order to escape adverse weather. The worm then empties the body of soil, then it excavates a chamber in which it coils itself up and remains dormant until more favourable conditions set in.the walls of the chamber are often lined with minute stone.

Useful invertebrates.

It is very doubtful that earthworms do any harm to the root of plants that are healthy { with exception of some non-native species, particularly some species that occur in North America } as for an example.

It is certain however, that the common European earthworm in its natural environs does in fact do much good by maintaining the soil in a state suitable for vegetation. Their burrows serve as ventilation tubes down which air can travel and become available for respiration by the roots, while at the same time they open up drainage channels and prevent the surface from becoming water logged. The roots too, find an easy way through the soil. However perhaps the most important aspect of their work is, done by tilling the soil bringing up the deeper layers up to the surface and the air.

Studies have revealed that worms are estimated { through sheer numbers} to move about 28 tons of soil annually per every acre. When it is considered that pasture land and all land laid down to grass of any kind that can not be ploughed or cultivated, it is evident that the work done by these industrious creatures is immense

Brandling worm is a species of dung heaps and rarely found in soil unless the soil is well manured.

Courtesy of M Dugaleana

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